It is at this time that squad depth is pushed to its very limit, a time when a team aspiring to the Premier League can be undone by injuries or suspensions in key positions that affect so many games in such a short period of time.
Goal takes a look at how the 'Big Six' compare in terms of strength in depth. Is there enough quality in each team's second-string XI to rotate and still compete?
|ARSENAL SQUAD DEPTH
That Arsene Wenger's side has maintained its impressive form to top the table at this middle stage is a testament to the improvements – some major, some subtle – that have been made to the squad. Yet there are undoubtedly areas in which the club is stronger than others.
Though the summer arrival of Mesut Ozil has dimmed Santi Cazorla's shine a little, it has proved a necessary addition to both spice up the attacking midfield and bolster the numbers therein. Key players behind the striker can afford to be rested or rotated now, with the north Londoners boasting arguably the most extensive list of top talent in that position outside of Chelsea. That, at least, is a comfort after the ever-so-impressive Aaron Ramsey was ruled out of the festive matches.
If, however, Olivier Giroud was to fall down the stairs on Saturday morning – or, as he has threatened to do recently, collapse from exhaustion – Wenger would find himself in a critical bind. Nicklas Bendtner is his only direct backup at center forward and, willing though the Frenchman may be to use him, the Denmark international is nearly as far below the standard required as he thinks he is above it. No surprises, then, that the Arsenal boss is surveying high-profile strikers for January recruitment.
There are secondary concerns on the defensive side. Though the Gunners have been much better at the back this season, primarily thanks to the swiftly improving partnership between Per Mertesacker and Laurent Koscielny, an under performing Thomas Vermaelen is the only other senior center back around and Wenger could quickly find himself having to draft Bacary Sagna uncomfortably into the middle if things go wrong.
Meanwhile, while not playing every game, Mathieu Flamini has been unexpectedly important this term and Mikel Arteta cannot offer the same kind of defensive midfield option. Though Arsenal has coped well enough with rotating the former AC Milan man this term, a game in which the club needs him but is unable to field him could be disastrous.
|MAN CITY SQUAD DEPTH
Increasingly, it looks like he is and it does look like the 2011-12 champion is the best-equipped to deal with the fatigue and necessary rotation of the festive schedule.
Though presently main man Sergio Aguero is on the treatment table, Pellegrini has still got Stevan Jovetic to fully introduce after an injury-hit first few months at the Etihad Stadium. Even further from the action is John Guidetti, whose lack of minutes is unfortunate given his previous success out on loan. City fans should hope to see more of them both in the winter scrum.
It is the back line which has seen the most absenteeism of late, with the likes of Pablo Zabaleta, Micah Richards and Matija Nastasic in and out of the physio room. Zabaleta returned, though not without bumps and bruises, against Liverpool but a longer-term problem might set hearts fluttering at Eastlands. In the middle, captain Vincent Kompany has been disrupted of late but is starting to flourish again with regular action – any new injury would leave the decidedly suspect Martin Demichelis with more responsibility than would be wise.
Pellegrini's midfield, however, is perfectly balanced for numbers – Javi Garcia and Jack Rodwell covering the center while the likes of David Silva, Jesus Navas and Samir Nasri rotate the wider attacking positions. Each offers distinct attributes, allowing plenty of flexibility during the fixture crush.
|CHELSEA SQUAD DEPTH
While some have been disappointed by the reality of their performances when the squad promises so much, the upshot is that the Blues could handle all kinds of injuries and rotation and end up with more or less the same results with whatever combination they are forced to field. The awkward handling of Juan Mata has allowed fleeting spotlight efforts from Willian and Andre Schurrle, while Kevin De Bruyne remains a frustratingly restricted figure.
The same can be said for the forward line – whichever of Samuel Eto'o, Fernando Torres and Demba Ba gets picked up front delivers the consistently average. Mourinho's irritation with his non-striking strikers is plain but, in terms of depth, the absence of any one center forward would not derail the current operations.
If there are concerns, it may be in defense. On paper, Chelsea is almost perfectly stocked behind the midfield, with two left backs, four center backs and one right back. But Branislav Ivanovic, arguably the club's best center back, has been the man stuck out on the right, while the team's specialist right back, Cesar Azpilicueta, has been displacing both Ashley Cole and Ryan Bertrand on the left.
Youngsters like Nathan Ake are available should disaster strike and the Blues need bodies to fill in but Mourinho is at risk of creating depth problems if his recent selections are the blueprint for how he sees the long term.
|LIVERPOOL SQUAD DEPTH
The Reds have coped admirably already this season with the respective absences of, first, Luis Suarez and, now, Daniel Sturridge, though the festive period has already begun testing that resolve even further.
For as long as Suarez remains fit and mining this utterly irrepressible vein of form, Liverpool will remain a threatening attacking prospect for any team. But, with any dip, the deficiencies in depth will quickly shine through.
The club's most direct backup striker, Iago Aspas, has made almost no impact since joining from Celta Vigo in the summer and there is persistent talk of a potential loan switch to Swansea City on the cards. Take him away and raw teenager Samed Yesil is the next cab off the rank – every other option would be an awkward fill-in.
Raheem Sterling's winter renaissance has been a vital plus point but Victor Moses has disappointed and Luis Alberto is a long way from completing his adaptation to English football. Things could go very poorly up front if, 10 minutes into the game against Chelsea on Sunday, Suarez pulls a hamstring.
Rodgers, then, must surely look to reinforce his attack as early in January as possible, with Sturridge not likely to be back long before the end of the month. At least his midfield is not looking so desperate – as Steven Gerrard recovers from a hamstring problem, Jordan Henderson has stepped up in remarkable style. The Reds captain was pictured before Christmas being put through his paces in training earlier than expected and a swift return should see the team's engine room sufficiently equipped to last the winter.
|MAN UTD SQUAD DEPTH
David Moyes is not short of bodies in the center of the pitch but quality he most certainly lacks. Aside from Michael Carrick, who himself is below last season's high standards, there is little on offer, particularly as Marouane Fellaini has appeared so intimidated by his big-money transfer – and both have had their own winter injuries.
While, like Chelsea's attacking midfield, this means that changes are less likely to diminish the club's overall output, the baseline is lower for the Red Devils here. That much is reflected by their lowly seventh place.
Indeed, there are only three specific positions where depth could really potentially bite for United – goalkeeper, left back and center forward.
Between the posts, David de Gea and Anders Lindegaard previously spent a season fighting it out for supremacy but the Spaniard has grown into a fine No.1, culminating in his anointment into the PFA Team of the Year last term. Now, an enforced change would be noticeable.
A similar effect would be felt on the left, where Patrice Evra is not what he once was but remains much more than Alexander Buttner has ever threatened to be. Meanwhile, up front, Danny Welbeck and Chicharito are good but 21 goals attest to the fact that they are a step down from Wayne Rooney and Robin van Persie.
Everywhere else, Moyes can chop and change with no serious recoil. Nemanja Vidic and, particularly, Rio Ferdinand are increasingly being phased out as Jonny Evans assumes greater responsibility at the back, while Phil Jones's latest injury comes as something of a blow. Either in defense or midfield, the time is ripe for him to step into a bigger role.
|SPURS SQUAD DEPTH
A flat four of Nacer Chadli and Gylfi Sigurdsson flanking Lewis Holtby and Christian Eriksen can be nothing other than a short-term gamble designed for a morale boost against a managerless team – if he intends to field an engine room without an even vaguely defensive presence, Sherwood's 18-month contract will last considerably less than that.
What is clear, at least, is that Spurs have more attacking midfielders than they know what to do with. The most obvious example is Erik Lamela, who was foolishly deployed on the right of a flat four against Southampton. The Argentine's struggles look set to be exacerbated, not alleviated, by the sacking of Andre Villas-Boas.
But with Andros Townsend and Aaron Lennon also in the mix, Sherwood has no shortage of pegs, whether or not he intends to force them into the right holes. With back-to-back early January tests against Manchester United and Arsenal to come, rotation is inevitable but entirely feasible.
Up front, a persistence with Roberto Soldado and Emmanuel Adebayor as a front two would necessarily prompt some swift shopping upon the turn of the year. Jermain Defoe, not rated by the new coaching regime, looks likely to depart for Toronto in January, which could mean that at least two new strikers are required to balance the squad. Before then, however, Sherwood will surely have to juggle, perhaps doing without his preferred pairing while the matches come thick and fast.
At the back, injuries have bitten badly already and could continue to frustrate. That Jan Vertonghen, Spurs' best center back, has so often had to deputize for the injured Danny Rose at left back is a concern, as is the necessity for Etienne Capoue to drop back from midfield.
Fitness has been the problem in the middle but, at fullback, it is simply a lack of quality cover and a relapse for Rose or an injury to Kyle Walker (who has started every Premier League game so far) would prompt a mini-crisis.
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